This invention relates generally to transducers. More particularly, the invention relates to a 1.5 dimensional ultrasonic transducer array suitable for use in medical imaging, as well as to methods of transducer use and construction.
Transducers are devices that convert electrical energy to mechanical energy, or vice versa. A common application of transducers is in ultrasonic imaging, which is often used in medical applications, non-destructive testing, and the like.
Transducers used for medical imaging typically include one or more transducer elements that may be matched to and driven by electronics connected to the transducer via a coaxial cable or the like. In an ultrasonic imaging application, for example, a typical transducer suitably converts an electrical signal generated by the electronics into mechanical vibrations (e.g. ultrasonic sound waves) that may be transmitted and reflected through the human body. The vibrations may be produced by one or more piezoelectric elements that suitably convert the electrical charge to acoustic (i.e. sound) energy. The transducer elements may also receive acoustic energy, which may be converted into electrical signals that may be processed by the attached electronics.
Frequently, transducers are sub-divided into transducer elements that may be individually and uniformly arranged along a straight or curvilinear axis, for example. Each transducer element is typically driven by an electric potential to produce an individual ultrasonic wave from that particular element. Each transducer element may be made up of a piezoelectric (e.g. ceramic) layer, a conducting layer, and one or more acoustic matching layers, as described, for example, in U.S. Pat. No. 5,637,800 issued Jun. 10, 1997 to Finsterwald et al. and incorporated herein by reference. Each element may be acoustically isolated from each of the other elements to prevent cross-talk and other error signals. The most common transducer elements are typically manufactured and arranged in a one-dimensional linear array that allows each element to be individually addressable by the associated electronics.
The individual waves generated by the various transducer elements produce a net ultrasonic wave or beam that may be focused at a selected point. If an electric signal is applied simultaneously to each element, the wave produced is typically relatively flat. By applying an electric signal at different time intervals to different elements, the net wave produced may become angled. In various embodiments, the net ultrasonic effect may be modeled as a gaussian wave. This net effect ultrasonic wave can frequently be xe2x80x9ctunedxe2x80x9d or xe2x80x9csteeredxe2x80x9d to scan an image in an imaging plane by activating or deactivating individual elements of the transducer.
The 1-D array of piezoelectric transducer elements typically allows the beam of ultrasonic energy to be focused only in the azimuth (i.e. the lateral and axial directions) of the imaging plane, and not in the elevation plane. Objects that are not in the azimuth imaging plane of the beam generally exhibit lower resolutions because the 1D array cannot typically steer the beam in planes other than the azimuth.
The current shift to digital beamforming technology holds promise for regular and rapid increases in the number of channels in a medical imaging transducer. A common implementation of a 1D transducer typically utilizes 128 elements, while a fully sampled two-dimensional aperture typically utilizes of the order of 10000 elements. Additional channels typically result in additional expense and complexity, so it is of interest to evaluate how much performance can be improved with a moderate increment in channel count.
Many conventional 1-D phased array probes have very good lateral and axial resolution. This has been achieved by improvements in transducer technology, by the use of more sensitive pre-amplifiers, and better matching between the transducer elements and the transmit-receive electronics. One aspect of system performance that has received less attention in recent years, however, is that of beamwidth in the plane perpendicular to the imaging plane, often referred to as the xe2x80x9celevation beamwidthxe2x80x9d or xe2x80x9cslice thicknessxe2x80x9d. There are two main reasons why slice thickness has received less attention than either lateral or axial resolution. First, changes in elevation beam width do not typically affect the display of a B-scan image as dramatically as changes in lateral and axial resolution. Second, building transducer arrays with the required elevation properties has been difficult since the already small elements must be further subdivided and independently controlled.
In order to make adjustments to the elevation beam width, multi-dimensional (e.g. 1.5-D and 2-D) arrays with additional beam-forming elements have been created to provide improved dynamic focusing and apodization. One technique for creating a multidimensional array involves the creation of additional elevation aperture strips within the transducer element. A one-dimensional transducer array typically utilizes 128 elements in the imaging plane that may be arranged in a single row. A 2-D array typically includes elements arranged into rows and columns with an elevational pitch that approaches an acoustic wavelength so that the beam may be steered and focused in both azimuth and elevation directions. A 1.5-D array is similar in that transducer elements are arranged into aperture and elevation strips, but that the elevational pitch remains relatively large such that beam focusing, but generally not beam steering, is possible in the elevation axis.
The creation of 1.5-D and 2-D arrays typically poses several problems. Adequately isolating aperture strips electrically and acoustically is one problem. U.S. Pat. No. 5,920,972 issued Jul. 13, 1999 to Palczewska et al. and incorporated herein by reference discloses a method of acoustically and electrically isolating individual aperture strips that uses a patterned conductive metallization bridge over the individual aperture strips to provide the electrical connections for each strip. This method, however, typically produces unwanted intra-element cross talk (e.g. electrical or acoustic interference between adjoining transducer elements).
A second problem common in multi-dimensional transducer arrays involves providing a reliable method of interconnecting the aperture strips. U.S. Pat. No. 5,617,865 issued Apr. 8, 1997 to Palczewska et al. and incorporated herein by reference, discloses a multidimensional array interconnecting aperture strips with a two sided flex circuit laminated over the piezoelectric, ceramic layer of the transducer. This method typically produces unwanted reflections from the flexible printed circuit and interferes with the pulse-echo response. Additionally, current methods for adequately isolating and interconnecting aperture strips are complicated and costly. U.S. Pat. No. 5,704,105 issued Jan. 6, 1998 to Venkataramani, et al. and incorporated herein by reference, for example, discloses another technique for creating 1.5-D and 2-D transducer arrays, but the technique described therein is complicated to implement and may not adequately isolate the various elements. It is therefore desirable to develop methods capable of efficiently creating a multidimensional array with adequately isolated and interconnected aperture strips.
According to various aspects of the invention, a transducer is manufactured by providing a substrate assembly, making aperture isolation cuts in the substrate assembly in a first direction, making minor element cuts in the substrate assembly in a second direction, positioning a plurality of signal lines (such as a flex circuit) on the substrate assembly such that the plurality of signal lines is aligned with said minor element cuts, and making major element cuts in the substrate assembly in the second direction after said plurality of signal lines is positioned.
Various aspects of the invention also include a multi-dimensional transducer having a plurality of elements, wherein the transducer includes a conductor; a piezoelectric assembly assembled with said conductor and having a first plurality of cuts in a first direction; and
a matching layer assembly having a second plurality of aperture cuts in the first direction, wherein the matching layer is coupled to the conductor opposite the piezo-electric assembly such that the first and second pluralities of elevation cuts are aligned to isolate the plurality of elements in an elevation dimension.